1. Field of the Invention
This invention relates to the art of making printed circuit boards by stamping the circuit board elements from a metal foil.
2. Description of the Prior Art
The prior art shows various devices and methods for stamping out from a foil sheet a circuit pattern for a printed circuit board. The two main methods used in the prior art for making circuit boards by die stamping are: (a) by use of a flat face die and (b) by use of a knife edge die.
For example, in U.S. Pat. No. 3,678,577, entitled, "Composite Structure and Method of Making the Same", by Walter Weglin and Charles W. Wildebour, issued July 25, 1972, there is disclosed a method of engaging a foil sheet with a flat-faced die to shear out a circuit pattern. Simultaneously heat is applied to the foil to cause a thermal setting adhesive between the foil and a dielectric base to bond the sheared foil sections to the substrate. As another example of the prior art, U.S. Pat. No. 2,986,804, to Greenman et al. discloses the use of a die element having an extended portion to also form holes in the dielectric for terminals. Further examples of the prior art are shown in Greenman et al, U.S. Pat. No. 2,988,839; Spiwak et al., U.S. Pat. No. 3,301,730; Anderson, et al., U.S. Pat. No. 3,340,606; and British Pat. No. 745,773.
With regard to making circuit boards by die stamping with a flat face die, one of the problems associated with that process is that it is not possible to make circuit boards where the circuit elements are any closer than about one-tenth of an inch from each other (measured center line to center line). When it is attempted to make circuit boards with a flat face die with the circuit elements closer than one-tenth of an inch, the stamping die is simply not able to shear out the circuit elements. Application of greater pressure to attempt to accomplish the shearing merely results in crushing the substrate onto which the circuit elements are to be formed,
The use of knife edge dies in stamping out circuit components from a foil sheet is shown, for example, in Petri, U.S. Pat. No. 3,015,718, which illustrates a heated die having two knife edges to cut out the circuit element. By applying pressure and heat from the die, a thermal setting adhesive positioned between the foil material and the substrate causes the foil circuit element to be bonded to the substrate. One of the advantages of having a knife edge die is that the knife edge is better able to cut out the foil sections. However, it is difficult to keep the knife edge sharp, and as the knife edge becomes dull, it will oftentimes stamp out thin ribbons of foil at the edge of the circuit elements, and these sometimes remain on the circuit board and cause it to short out. Another problem associated with knife edge dies is that when circuit elements are being formed on a thin film, such as a plastic sheet several thousandths of an inch thick, the knife edge sometimes penetrates through the thin film so as to damage the same.
Other examples of the prior art which show various forms of a knife edged die are: Courtenay, U.S. Pat. No. 1,646,613; Franklin, U.S. Pat. No. 2,647,852; Franklin, U.S. Pat. No. 2,622,054; and Franklin, U.S. Pat. No. 2,753,619.
Other patents showing various foil stamping methods are: Debacher, U.S. Pat. No. 1,187,510; Choate, U.S. Pat. No. 1,406,538; Greenman et al., U.S. Pat. No. 2,272,003; and Anderson et al., U.S. Pat. No. 3,052,832.
It is an object of the present invention to accomplish the practical manufacture of circuits by a die stamping process, either on a board or a thin film dielectric, where the circuit elements are relatively closely spaced and relatively long die life is achieved in the manufacturing process.